German foreign minister Heiko Maas said today that Russian blockade of the passage into the Sea of Azov was not acceptable and urged both Russia and Ukraine to de-escalate tensions.

Heiko Maas called for the opening of the blockade as tensions simmered between Russia and Ukraine.

Russia's FSB security service said its border patrol boats had seized two small Ukrainian armoured artillery vessels and a tug boat after opening fire. The security agency said three Ukrainian sailors were injured in the clash.

The Ukraine vessels had allegedly ignored warnings sent by the Russian navy, the officials claimed.

Tensions between the two countries have been simmering since Russia annexed Ukraine's Crimea in 2014 leading to worldwide condemnation. Ukraine asked the international community to punish Russia as the latest skirmish threatened to disrupt the uneasy peace.

Meanwhile, the UN will meet on Monday over the latest development on the request of both Russian and Ukrainian officials. Both the European Union and NATO urged both countries to exercise restraint and de-escalate the situation.

NATO said it will hold an emergency meeting with Ukrainian officials at alliance headquarters in Brussels on Monday.

Canada and Denmark sided with the Ukraine government as Canadian foreign minister Chrystia Freeland asked Russia to release the captured vessels.

Meanwhile, the FSB has said Russia has opened a criminal case against Ukraine for ships illegal entry into Russia's territorial waters.

A bilateral treaty gives both Russia and Ukraine the right to use the Sea of Azov.

Russia had built road bridge linking southern Russia where the Kerch Strait is located after annexing Crimea. Ukraine has key ports in the Sea of Azov which has become the latest tug of war between the two countries.

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Russia's FSB security service said its border patrol boats had seized two small Ukrainian armoured artillery vessels